Experimental examination of wide-area current differential backup protection employing broadband communications and time transfer systems

Based on the authors' previously proposed wide-area current differential backup protection utilizing broadband packet communications and time synchronous systems for achieving better selectivity, smaller outage areas and faster operation times than conventional distance backup protection, experimental microprocessor-based protection devices have been examined with respect to both telecommunication and protection functions. The experimental wide-area protection system consists of one central equipment (CE) unit and three terminal equipment (TE) units connected by a 155-Mbps ATM backbone network with a LAN interface and GPS time acquisition and features a simplified and effective method for expanding protection zones after primary or minimum-zone protection operation. In an AC power system simulator configuring a busbar and a power line, each TE at a circuit breaker location transmits sampled current data to the CE and receives a tripping command initiated by it, and operate satisfactorily in various states of power system and telecommunications.